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What are the components included in an entity declaration in VHDL?
What are the components included in an entity declaration in VHDL?
An entity declaration includes the entity name and a list of interface ports.
State two rules for naming entities in VHDL.
State two rules for naming entities in VHDL.
The first letter must be an alphabet character, and special characters other than underscore are not allowed.
Explain the purpose of the 'buffer' signal mode in VHDL.
Explain the purpose of the 'buffer' signal mode in VHDL.
The 'buffer' signal mode is used when a signal needs to be temporarily stored.
What is the purpose of the 'USE' clause in VHDL?
What is the purpose of the 'USE' clause in VHDL?
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What are the three commonly used libraries in VHDL design, and why are they important?
What are the three commonly used libraries in VHDL design, and why are they important?
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What are the two popular hardware description languages mentioned, and what programming languages are they based on?
What are the two popular hardware description languages mentioned, and what programming languages are they based on?
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Describe the primary purpose of Hardware Description Languages (HDLs).
Describe the primary purpose of Hardware Description Languages (HDLs).
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What are the three types of modeling supported by VHDL?
What are the three types of modeling supported by VHDL?
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What does the 'Library Declaration' in VHDL allow a designer to do?
What does the 'Library Declaration' in VHDL allow a designer to do?
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Explain the flexible design methodology offered by VHDL.
Explain the flexible design methodology offered by VHDL.
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What is one benefit of writing Test Benches in VHDL?
What is one benefit of writing Test Benches in VHDL?
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What is the purpose of the configuration section in a VHDL project?
What is the purpose of the configuration section in a VHDL project?
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What key feature does VHDL provide for large-scale designs?
What key feature does VHDL provide for large-scale designs?
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What is the primary purpose of the entity declaration in VHDL?
What is the primary purpose of the entity declaration in VHDL?
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List three commonly used signal types in VHDL.
List three commonly used signal types in VHDL.
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Explain the difference between dataflow and behavioral architecture in VHDL.
Explain the difference between dataflow and behavioral architecture in VHDL.
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What is the unique characteristic of NAND and NOR operators in VHDL?
What is the unique characteristic of NAND and NOR operators in VHDL?
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Identify the highest precedence logical operator in VHDL and explain its relevance.
Identify the highest precedence logical operator in VHDL and explain its relevance.
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What role do assignment operators play in VHDL?
What role do assignment operators play in VHDL?
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How do relational operators function in VHDL?
How do relational operators function in VHDL?
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What is included in the port section of an entity declaration?
What is included in the port section of an entity declaration?
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Study Notes
DE Module 5: VHDL Introduction
- VHDL (Very High Speed Integrated Circuits Hardware Description Language) is a hardware description language used to describe hardware.
- Verilog is another popular hardware description language that is based on the C language.
- VHDL was developed by the U.S. Department of Defence.
- VHDL follows IEEE Standard 1076-1987, 1993 and 200x
- Verilog has an IEEE Standard 1364-1995, 2001 and 2005
Contents
- Different design styles are part of the module.
- Implementation of adder, subtractor, multiplexer and flip-flop are covered.
Introduction
- Hardware Description Languages (HDL) are used to describe hardware.
- VHDL and Verilog are two popular HDLs.
Applications of HDL
- Modeling and documenting digital systems using different abstraction levels (behavioral, structural, etc.).
- Verifying design circuits.
- Converting designs from higher abstraction levels to lower abstraction levels.
Features of VHDL
- Describes, models and verifies a system before synthesis.
- Allows description of concurrent systems.
- Is multipurpose.
- Supports flexible design methodologies (top-down, bottom-up or both).
- Supports various modelling types (behavioral or sequential, dataflow, structural).
- Makes large-scale design easier with components, functions, procedures, packages and configuration.
- Allows test benches to be written in the same language as the circuits.
- Allows circuits to be verified before synthesis.
Structure of VHDL Code
- VHDL code structure has four key parts:
- Library Declaration
- Entity
- Architecture
- Configuration
Library Declaration
-
To make a package visible in the design, two declarations are required:
- Library Clause
- Use Clause
-
A design typically needs libraries from at least three different libraries: (e.g., ieee, std, work).
Entity
-
Describes the external view of the device.
-
Includes at least one architecture associated with it.
-
Declares the name and list of interface ports.
-
Ports represent signals used for communication with other devices or terminals.
-
Input and output ports are specified within the entity.
Entity Syntax
- The basic structure of an entity definition:
- ENTITY entity_name IS
- Port(
- Port_name : signal_mode signal_type;
- Port_name : signal_mode signal_type )
- END entity_name;
- Port(
- ENTITY entity_name IS
Rules to write entity name
- The first letter of the entity name must be an alphabet.
- Special characters are allowed only as underscores.
- Two consecutive underscores aren't allowed.
- The entity name cannot end with a special character.
Signal Modes
- Describes how a signal is used (input, output, inout, buffer) within the design.
- For example, counter state, shift register state.
Signal Types
- Commonly used signal types:
- bit
- bit_vector
- std_logic
- std_logic_vector
Entity Declaration of a Circuit
-
Example of entity declaration for a circuit with inputs A, B, S and outputs X, Y:
- entity my_ckt is
- port (
- A: in bit;
- B: in bit;
- S: in bit;
- X: out bit;
- Y: out bit);
- port (
- end my_ckt;
- entity my_ckt is
Write entity declaration for NOR gate
- entity nor_gate is port (A, B: in STD_LOGIC; Y: out STD_LOGIC); end nor_gate;
Architecture Body
- A VHDL architecture defines how the hardware entity's behavior is implemented.
- There are three ways to implement this architecture: dataflow, behavioral, and structural.
Syntax of Architecture
- The syntax of an architecture body includes a declarative part and a statement part.
VHDL Operators
- Several types of operators are used in VHDL (assignment, logical, relational, shift, adding, multiplying and miscellaneous).
Assignment Operators
- Used to assign values to signals, variables, and constants.
- The assignment operator
<=is used to assign a value to a Signal and the assignment operator:=for variable, constant or Generic.
Logical Operators
- The seven logical operators use bit operands and produce bit results.
- Examples include AND, OR, NAND, NOR, XOR, XNOR, NOT.
Relational Operators
- VHDL supports equality and inequality operators.
- Operators include: =, /=, <, <=, >, >=;
Shift Operators
- Examples include Shift left logical, Shift right logical, Shift left arithmetic, Shift right arithmetic, Rotate Left, Rotate Right.
Adding Operators
- Includes addition, subtraction, and concatenation.
- Example a & b where & is used for concatenation.
Multiplying Operators
- Includes multiplication, division, Mod (modulus operator), Remainer.
Miscellaneous Operators
- Functions include Absolute, Exponentiation, Negation.
Data Flow Style
- Example VHDL code for a NOR gate in data flow style, which describes how the hardware functions.
Write VHDL Code for Half adder
- Example of Half adder code in data flow style .
Behavioral Style (Sequential Execution)
- This describes the behavior of the hardware through a series of sequential steps like if-then-else, and elsif statements.
VHDL Code for Half Adder in Behavioural Style
- VHDL code for half adder design using if-then-else statements (a behavioural approach).
Problems
- This module describes how to implement a 4-1 multiplexer in behavioural style using if-then-else statements.
Attributes
- Attributes are used to increase the flexibility of code.
- Useful for handling different data types/ sizes for code.
- Important attributes:
Clk'EVENT,RISING_EDGE(clk)
D Flip-Flop
- VHDL code structure for D flip flop.
JK FF using variable
- VHDL code structure for JK flip flop that uses variable for logic implementation.
SR FF using variable
- VHDL design using variables for SR Flip-flop logic.
T FF using variable
- VHDL design using variables for T Flip-flop logic.
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Description
This quiz covers the fundamentals of VHDL, a hardware description language used for describing digital hardware. It introduces different design styles, essential components like adders and multiplexers, and compares VHDL with Verilog. Explore the applications and features of HDL in digital system design.
